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Name ______

Title: Salt Water Taffy

Purpose: To study the formation of an amorphous solid.

Background: Sucrose, whose formula is C12H22O11 (Figure 1), is only one of many compounds called sugars, which fall into an even larger class of compounds called carbohydrates. Sucrose is found naturally in most plants, but plants such as sugarcane and sugar beets have especially high concentrations. Sucrose is actually a disaccharide, which is made of two simpler sugars bonded together, fructose and glucose.

Figure 1. The structure of sucrose, that results from the linkage of the monosaccharides glucose and fructose.

If you look closely at dry cane sugar, you will notice it comes in little blocks with shinny or highly reflective surfaces. These sugar crystals result from the regular repeating three- dimensional pattern of sucrose molecules. Under a microscope, you can see that sugar crystals are oblong and slanted at both ends, reflecting how the molecules forming the regular repeating pattern in the solid state produce a unit cell.

When you add sugar to water, the sugar crystals dissolve to form a solution. But you can’t dissolve an infinite amount of sugar into a fixed volume of water. When as much sugar has been dissolved as possible, the solution is said to be saturated. The saturation point is directly related to temperature, with more sugar dissolving at higher temperatures. When you make candy, you mix and heat sugar, water, and various other ingredients to high temperatures. At these temperatures, the sugar remains in solution, even though much of the water has boiled away. But when the candy is through cooking and begins to cool, there is more sugar in solution than is normally possible at room temperature and the solution is said to be supersaturated. Stirring or jostling of any kind as well as the addition of a seed crystal can cause the sugar to begin crystallizing. The fact that sugar solidifies into crystals is extremely important in candy making. There are basically two categories of candies - crystalline (candies that contain crystals in their finished form, such as fudge), and noncrystalline, or amorphous (candies which do not contain crystals, such as lollipops, taffy, and caramels). Recipe ingredients and procedures for noncrystalline candies are specifically designed to prevent the formation of sugar crystals, because they give the resulting candy a grainy texture.

Name ______

One way to prevent the crystallization of sucrose is to make sure that there are other types of sugars—usually, fructose and glucose—to get in the way. Large crystals of sucrose have a hard time forming when molecules of fructose and glucose are present. Crystals are similar to Legos™, with molecules locking together to form a larger structure. If some of the molecules are a different size, shape, or have different types of intermolecular forces of attraction, not all of the molecules will fit together to form a crystal. A simple way to get other types of sugars is by adding an acid to the recipe. Acids such as lemon juice or cream of tartar cause sucrose to break up (this is called acid catalyzed hydrolysis) into its two simpler components, fructose and glucose. Another way is to add a nonsucrose sugar, such as corn syrup, which is mainly glucose. Some lollipop recipes use as much as 50% corn syrup to prevent sugar crystals from ruining the texture. Fats that are hydrophobic can be added to candy and serve a similar purpose. Therefore, ingredients such as butter help interfere with crystallization. Toffee owes its smooth texture and flavor partly due to a large amount of butter fat in the mix.

Materials:1 You will use 2 cups sugar, 2 tablespoons cornstarch, 1 cup light corn syrup, 2 teaspoons glycerin (optional), 3/4 cup water, 2 tablespoons butter, 1 teaspoon salt, 1/4 to 1 teaspoon flavoring (such as vanilla, lemon, maple, or mint), 3 drops food coloring (optional), a large (3- to 4-quart) saucepan, a wooden spoon, a candy thermometer, a pastry brush, waxed paper or plastic wrap, a cookie sheet, greased scissors or butter knife.

Procedure: Combine the ingredents and use the materials as indicated below.

1. Mix together sugar and cornstarch in the saucepan. 2. Use a wooden spoon to stir in the corn syrup, glycerin (optional), water, butter, and salt. Place the saucepan over medium heat and stir until the sugar dissolves. 3. Continue stirring until the mixture begins to boil, then let cook, undisturbed, until it reaches about 270° F.2 Wash down the sides of the pan with a pastry brush dipped in warm water while the syrup cooks. 3. Remove the saucepan from the heat and add the food coloring and flavoring. Stir gently, then pour into a shallow greased cookie sheet to cool. 4. Wash your hands with soap and water. When the taffy is cool enough to handle, you and a partner should grease your hands with oil or butter and pull the taffy until it is light in color and has a satiny gloss. You should pull the taffy for about 10 minutes. 5. Roll the pulled taffy into a long rope, about 1/2 inch in diameter, and cut it with greased scissors into 1-inch-long pieces. Let the pieces sit for about half an hour before wrapping them in plastic wrap and twisting the ends of the wrapper.

1 1 cup = 8 fl oz; 1 cup = 237 mL; 1 tablespoon = ½ fl oz; 1 teaspoon = 1/6 fld oz 2 °F = (°C x 9/5) + 32

Name ______

Data and Analysis Answer the following questions.

1. Briefly define the following terms.

a. Amorphous

b. Crystalline

c. Intermolecular

d. Unit cell

e. Solution

f. Supersaturated

2. When you are finished, chew and taste your taffy. Compare the texture to that of the cane sugar that you started with and briefly explain the change that has occurred on the molecular level.

Name ______

3. Calculate what the equivalent of 270°F is on the celceius scale. Show work.

4. Convert the following volumes to the metric equivalent using dimensional analysis.

a. 2 cups to milliliters

b. 2 tablespoons to milliliters

c. 2 teaspoons to milliliters

Name ______

Answers

1. (a) Amorphous – not having a regular repeating pattern on the molecular level; (b) Crystalline – having a regular repeating pattern in three dimensions on the molecular level; (c) Intermoleculat – between molecules; (d) Unit cell – the smallest three dimensional repeating pattern in a crystalline solid; (e) Solution – a homogeneous mixture, usually liquid, of a solvent and solute; (f) Supersaturated – a solution that has more solute dissolved than it would normally hold at a particular temperature. 2. The taffy is chewy, where as the cane sugar is hard and crunchy. 3. 132°C 4. 500 mL 5. 30 mL 6. 10 mL